n.(名词)

1. [U]必要(性); (迫切)需要circumstances that force one to do sth; state of being necessary
2. [C]必需品necessary thing
3. [S]自然规律natural law that is seen as governing human action

demandn.要求；需求v.要求；查问；需要

needv.需要；必需n.需要；必要；缺乏aux.需要，必须（无时态、人称变化，后与不带 to 的动词不定式连用，多用于疑问句和否定句）

requirementn.必要条件；要求

unnecessaryadj.不必要的；多余的

chancen.可能性；机会；偶然性v.偶然发生；碰巧；冒 ... (的险)

1. Necessity is the mother of invention.
   需要是发明之母。
2. Want and necessity break faiths and oaths.
   匮乏和需要可以打破信仰和誓言。
3. Water is of vital necessity in the desert.
   在沙漠地区水是维持生命的必需品。
4. Food is a necessity, but wine is an extravagance.
   食物是必需品,而酒则是奢侈品。
5. The necessity for making decisions devolves on him.
   作出决策乃当务之急，此事必然地落在他身上。
6. That men would die was a matter of necessity; which men would die, though, was a matter of circumstance.
   人总有一死，这是必然的事，不过哪些人死，这是偶然的事。